Magnet structure



May 25, 1965 F. c. SKELTON, JR 3,185,899

MAGNET STRUCTURE Filed May 21, 1962 Il l l' Pg-2 I I/ pm. l,

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grani C. Skelton (jr. 11 (dwf/.7 l Z/...Q UTTGRNEYM/ United StatesPatent O 3,135,399 MAGNET STRUCTURE Frank C. Skelton, Ir., Beloit, Wis.,assigner to Warner Electric Brake & Clutch Company, South Beloit, Ill.,a corporation of Delaware Filed May 21, 1962, Ser. No. 196,372 3 Claims.(Cl. 317-158) This invention relates to a magnet adapted for use in amagnetic friction clutch or brake to force magnetic flux into and out ofan abutting face of a narrow magnetic armature and thereby draw thelatter into gripping engagement with the magnet pole faces. In View ofthe narrow width of the armature, it has been the practice heretofore tobevel the adjacent edges of the magnet pole pieces and fill theresulting V-shaped groove with non-magnetic material which separates thepole faces by a very narrow gap while securing the pole pieces rigidlytogether.

The primary object is to provide a separating filling of the abovecharacter which facilitates low cost manufacture of the magnet andinsures precise and uniform edgewise spacing of the pole faces by anon-magnetic gap of the desired narrow width.

A more detailed object is to separate the pole faces by a thin shimwhich is located in the initial assembly and becomes an integral part ofthe filling.

Other objects and advantages of the invention will become apparent fromthe following detailed description taken in connection with theaccompanying drawings, in which:

FIGURE l is a fragmentary diametrical sectional View of a frictionclutch embodying the novel features of the present invention.

FIG. 2 is an eight-times enlargement1 of a part of FIG. 1.

FIG. 3 is a perspective view of the ring forming the non-magnetic gap.

The improved filling construction is especially suited for use in afriction coupling of the general type shown in which driving and drivenmembers and 11 are frictionally coupled together by winding up a helicalspring coil 12 to contract a split friction band 13 around surfaces 14and 15 on the members axially spaced along the clutch axis. The coil isformed of wire of magnetic material and narrow rectangularcross-section, one end being anchored at 16 on the driven member. Theopposite end turn 17 constitutes the armature of a magnetic pilot clutchhaving annnular pole pieces 18 and 19 carried by the driving member 10and secured together in closely spaced edge to edge relation with theirexposed faces 20 and 21 disposed flush with each other and closelyadjacent the axial face of the armature 17 which, by bending of the wireof the coil, is disposed in an axial plane.

The magnet pole faces are radially separated by a narrow gap 22 which isdisposed midway between the inner and outer edges of the armature. Attheir opposite ends, the pole pieces 18, 19 are formed with surfaces 23,24 which are concentric with the clutch axis and telescope with innerand outer legs of a stationary magnetic core 25 of U-shapedcross-section enclosing a multiple turn winding 26. When the latter isenergized, magnetic flux threads the toroidal path 27 which extendsaround the gap 22 and into and out of the inner and outer portions ofthe armature 17. The latter is thus drawn into gripping engagement withthe pole faces thereby developing a friction torque for winding up thecoil 12 to engage the clutch.

Rigid joining of the poles pieces 18, 19 is achieved by a ring 30 ofnon-magnetic material `such as bronze Patented May 25, 1965 "ice meltedand flowed as by a welding torch into a groove delined by opposedsurfaces 31, 32 on the pole pieces diverging away from each other froman apex 33 which is axially spaced a short distance away from the polefaces so as to leave cylindrical surfaces 34 on the opposed edges of thepole pieces. These surfaces are machined accurately so as to beprecisely concentric with the axis of the pole rings.

In accordance with the present invention, the gap 22 separating theedges 34 of the pole rings is formed of a thin strip 36 of shim stockusually about .006 of an inch thick bent into the form of a cylinder asshown in FIG. 3 and composed of brass or other non-magnetic metal whichwill bond with the metal of the filling 30 but will not be destroyedduring flowing of the latter into the groove 31, 32. The strip issubstantially wider than the edge surfaces 34 so that when one edgeportion 37 is disposed between these surfaces and flush with the polefaces 20, 21, the opposite edge portion 33 will extend well into theapex portion of the groove. In the welding of the lling into thisgroove, the molten bronze flows around the portion 3S and becomes bondedthereto.

With part of the strip thus firmly embedded in the lilling, the portion37 which forms the gap 22 will be held securely between the pole edgesand completely filling the space between the two with solid non-magneticmetal and of a thickness determined by that of the shim. The

latter wears away with the pole faces in service use but1L there is nopossibility of accumulating between the edge surfaces 34 any ironparticles that would afford paths for by-passing flux directly betweenthe pole pieces. By using a separate metal strip to form the gap 22, thewidth and the uniformity thereof are established with great accuracy andat low cost while providing a filling of the desired divergingcross-section. That is to say, the pole pieces are formed in simplemachining operations and no elaborate fixturing is required duringwelding of the filling into the groove.

I claim as my invention:

1. In a magnet construction, the combination of, a thin strip ofnon-magnetic metal, two magnetic pole pieces arranged edge to edge insurface abutment with opposite sides of one edge portion of said stripand having exposed end faces disposed in a common plane substantiallyflush with the edge of said one end portion, the edge surface of saidpieces opposite the other edge portion of said strip diverging away fromopposite sides of such portion so as to define a V-shaped groove dividedby such other edge portion of the strip and a rigid metal fillingdisposed in said groove and bonded securely to said other edge portionof the strip and the diverging side walls of said groove so as to unitesaid pole pieces and said strip into a rigid structure with said polefaces and the side surfaces of said pole pieces magnetically separatedby said one edge portion of said strip.

2. A magnet construction as defined in claim l in which the outer edgeof said strip forms with said pole faces an uninterrupted planarsurface.

3. A magnet construction as defined in claim 1 in which the thickness ofsaid strip is on the order of a few thousandths of an inch.

References Cited by the Examiner UNITED STATES PATENTS 2,739,684 3/56Meyer l92-84 2,798,581 7/57 Supitilov 192-84 2,857,998 10/58 Harter192--84 3,055,470 9/62 Pierce 192--84 JOHN F. BURNS, Primary Examiner.

FRANK SUSKO, Examiner.

1. IN A MAGNET CONSTRUCTION, THE COMBINATION OF, A THIN STRIP OFNON-MAGNETIC METAL, TWO MAGNETIC POLE PIECES ARRANGED EDGE TO EDGE INSURFACE ABUTMENT WITH OPPOSITE SIDESOF ONE EDGE PORTION OF SAID STRIPAND HAVING EXPOSED END FACES DISPOSED IN A COMMON PLANE SUBSTANTIALLYFLUSH WITH THE EDGE OF SAID ONE END PORTION, THE EDGE SURFACE OF SAIDPIECES OPPOSITE THE OTHER EDGE PORTION OF SAID STRIP DIVERGING AWAY FROMOPPOSITE SIDES OF SUCH PORTION SO AS TO DEFINE A V-SHAPED GROOVE DIVIDEDBY SUCH OTHER EDGE PORTION OF THE STRIP AND A RIGID METAL FILLINGDISPOSED IN SAID GROOVE AND BONDED SECURELY TO SAID OTHER EDGE PORTIONOF THE STRIP AND THE DIVERGING SIDE WALLS OF SAID GROOVE SO AS TO UNITESAID POLE PIECES AND SAID STRIP INTO A RIGID STRUCTURE WITH SAID POLEFACES AND THE SIDE SURFACES OF SAID POLE PIECES, MAGNETICALLY SEPARATEDBY SAID ONE EDGE PORTION OF SAID STRIP.